1. Field of the Invention
The invention relates to a bead inspection method and a bead inspection apparatus for inspecting the quality of a bead that is formed when a plurality of metal workpieces are joined by brazing.
2. Description of the Related Art
As for a related-art technology, brazing is known as a technique of joining a plurality of metal workpieces. For example, the brazing is a technique as shown in FIG. 21 in which a first workpiece M1 and a second workpiece M2 that are metal plates curved at about 90° are joined by placing the two workpieces M1 and M2 in contact with each other at their up-down-direction flat portions (flat portions extending in a vertical direction in FIG. 21) while a left-right-direction flat portion of the first workpiece M1 (a flat portion thereof extending in a horizontal direction in FIG. 21) is placed higher than a left-right-direction flat portion of the second workpiece M2 (a flat portion thereof extending in the horizontal direction in FIG. 21), and then introducing an alloy (solder) melted by laser or the like into a space S that is formed between the up-down-direction flat portion of the first workpiece M1 and a curved portion of the second workpiece M2 so as to form a bead B that extends between the up-down-direction flat portion of the first workpiece M1 and the curved portion of the second workpiece M2.
After the brazing as described above is performed, it is inspected whether or not the bead B has a predetermined strength. The inspection about the bead B includes measuring the throat thickness of the bead B (the smallest size of a dimension between the obverse and reverse surfaces of the bead B) and determining whether or not the throat thickness satisfies a certain criterion.
Since the throat thickness of the bead B is difficult to directly measure, the bead B of an extracted sample is cut and a throat thickness is measured on the cut cross-section. Therefore, an increased number of man-hours for the bead B inspection, an increased number of waste works, etc., are brought about, so that the cost for the inspection rises and therefore the manufacturing cost of the product increases.
Japanese Patent Application Publication No. 9-79833 (JP-A-9-79833) discloses a technology which employs a probe that moves in contact with a bead as an inspection object and that sends and receives ultrasonic waves, and which therefore non-destructively measures the throat thickness of the bead by using ultrasonic waves. However, the technology described in the literature JP-A-9-79833 is not able to obtain a desirable result when the inspection-object bead is small relative to the probe.